1. Field of the Invention
The invention relates to a method and apparatus for manufacturing ink jet printheads and the product printheads derived therefrom, and, more particularly, to a method and apparatus for film coated passivation of side walls of ink channels in ink jet printheads and printheads with ink channel side walls film coated by such method.
2. Description of the Related Art
Printers provide a means of outputting a permanent record in human readable form. A printing technique may generally be categorized as either impact printing or non-impact printing. A popular form of non-impact printing is referred to as ink jet printing. In ink jet printing, ink is ejected, most commonly by pressure, through a tiny nozzle to form an ink droplet that is deposited upon a paper medium. Such ink jet printing devices produce highly reproducible and controllable droplets, so that a droplet may be printed at a location specified by digitally stored data.
Most commercially available ink jet printing systems may be generally classified as either a "continuous jet" type ink jet printing system or a "drop on demand" type ink jet printing system. In a continuous jet type ink jet printing system, ink droplets are continuously ejected from the printhead and either directed to or away from the paper medium depending on the desired image to be produced. In such system, uniform ink droplets are formed from a stream of liquid issuing from an orifice. The ink stream in this type system is in continuous flow as a result of mechanically-induced pressure thereupon. A mechanism, often of an electromechanical material such as piezoelectric material, oscillates in response to an applied voltage to cause break-up of the continuous stream into uniform droplets of ink and to impart an electrostatic charge to the droplets. High voltage deflection plates located in the vicinity of the ejected ink droplets selectively control the trajectory of the ink droplets causing the droplets to hit a desired spot on the paper medium. Since a continuous flow of ink is employed in this type system, it is referred to as continuous.
In a "drop on demand" type ink jet printing system, ink droplets are ejected from the printhead in response to a specific command related to the image to be produced. The ink droplets are produced as a result of electromechanically induced pressure waves. The ink is typically saliently stored in a reservoir or channel. A volumetric change in the ink fluid so stored is then induced by the application of a voltage pulse to an electromechanical material, such as a piezoelectric material, which is directly or indirectly coupled to the fluid. This volumetric change causes pressure/velocity transients to occur in the fluid and these are directed so as to produce a droplet that issues from the reservoir or channel, typically through an orifice. Since the voltage is applied only when a droplet is desired, these types of ink jet printing systems are referred to as drop-on-demand.
The use of piezoelectric materials in ink jet printers is well known. Most commonly, piezoelectric materials are used in a piezoelectric transducer by which electric energy is converted into mechanical energy by applying an electric field across the material, thereby causing the piezoelectric material to deform. This ability to distort piezoelectric material by application of an electric field has often been utilized in order to interrupt or distort ink flow in a continuous type system or to force the ejection of ink from reservoirs or channels of drop on demand type systems.
One drop on demand type ink jet printer configuration which utilizes the distortion of a piezoelectric material to eject ink includes a printhead forming an ink channel array in which the individual channels of the array each have side walls formed at least, in part, of a piezoelectric material. In the typical case of such an array, the channels are micro-sized and are arranged such that the spacing between adjacent channels is relatively small. In operation of this type printhead, ink is directed to and resides in the channels until selectively ejected therefrom. Ejection of ink from select channels is effected due to the electromechanical nature of the piezoelectric side walls of the channels. Because piezoelectric material deforms when an electric field is applied thereacross, the side walls of selective channels may be caused to deform by applying an electric field across select ones thereof. The electric field may be so selectively applied by digital or other means. This deformation of side walls of select channels reduces the volume of the respective channels creating a pressure pulse in the ink residing in those channels. The resultant pressure pulse then causes the ejection of a droplet of ink from the front end of the particular channel adjacent side walls across which the electric field is applied.
Many ink jet printheads also include a cover plate fixedly mounted on the front end of the printhead adjacent ink channels. Extending through such a cover plate may be a plurality of orifices which comprise an array. In most ink jet printheads, each orifice in such an orifice array corresponds to one of the ink channels of the printhead. A cover plate is typically positioned abutting the printhead in a manner so that each orifice is in communication with a corresponding channel of the printhead. When a pressure wave is created in ink in a typical ink jet printhead due to electromechanical action or otherwise, an ink droplet is forcibly ejected from the ink jet printhead through the orifice. This type of orifice can form an appropriate ink droplet to create a desired impression as the droplet is thereby deposited on a paper medium.
In a typical configuration of an array of closely spaced channels the side walls of which are formed of electromechanical materials and across which side walls is selectively applied an electrical field to particular ones of the side walls, for example as in a drop on demand type ink jet printhead, the very close spacing between side walls of the channels and the conductive nature of fluid, such as ink, within the channels leads to problems with shorting of electricity. Electricity applied to select side walls of channels may short from select side walls to which electrical field is selectively applied, through the fluid within the adjacent channels, and to non-select side walls located adjacent the channels. This type of shorting can result in unintended deformation of side walls adjacent the particular select side wall causing the non-select side walls to also deform, for example causing ejection of ink from non-select adjacent channels in ink jet printheads. In ink jet printheads, unintended ejection of ink from adjacent channels distorts the intended print and reduces print quality due to irregular definition of print characters formed from the unintentionally ejected droplets. It would be an improvement over the prior art to have a method and apparatus to reduce or eliminate shorting of electrical field among select and non-select side walls of channels in a device, for example an ink jet printhead. This type of improvement in ink jet printheads would reduce ejection of ink from non-select channels, limiting ejection to those select channels have side walls across which electrical field is intentionally applied. To applicant's knowledge, a method for reducing shorting of this type, for example by film coated passivation of surfaces of side walls of ink channels, has not been practiced to date and an apparatus therefor and product therefrom has not heretofore existed.